For ease of illustration, the various techniques disclosed in this document are discussed below in the context of IEEE 802.11-based wireless networking. This context is described in the IEEE 802.11 specifications for wireless local area network (WLAN) media access control (MAC) and Physical Layer (PHY). However, those of ordinary skill in the art, using the teachings provided in this document, may implement the disclosed techniques in other wireless networks. Accordingly, references to techniques and components specific to IEEE 802.11 apply also to the equivalent techniques or components in other wireless network standards unless otherwise noted.
A WLAN is identified by its network name, which in IEEE 802.11 is known as a service-set identifier (SSID). An infrastructure basic service set (BSS) is defined in IEEE 802.11 as a single access point (AP) together with all its associated mobile stations, and is uniquely identified by its basic service-set identifier (BSSID). Since an AP is uniquely identified by its MAC address, the MAC address of the AP is typically used as the BSSID. BSSs may be connected to one another via networks denoted distribution systems (DS). Multiple DSs may be interconnected by routing devices. A subnetwork is a portion of a network that shares a common address component and operates at Layers 1 and 2 (physical and data link) of the OSI (Open System Interconnection) reference model. On TCP/IP (Transmission Control Protocol/Internet Protocol) networks, subnetworks are all devices whose Internet Protocol (IP) addresses have the same prefix. Routers, and the process of routing, operate at Layer 3 (network) of the OSI reference model. In IEEE 802.11 an Extended Service Set (ESS) includes two or more BSSs that use the same SSID, and is uniquely identified by an extended service set identifier (ESSID).
In order to enable a mobile station to be truly mobile, the mobile station is typically powered by a battery. Power consumption and battery drain are issues of concern.
It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity.